The present invention generally relates to disc drive apparatus, and more particularly relates to an improvement in the control of disc flutter and half frequency whirl to provide enhanced medium to transducer spacing and stabilization.
For successful magnetic recording, particularly at high densities, such as is currently employed in high density disc drive storage apparatus, there should be a predictable constant space in between a record medium and a transducer which is used to access the record medium for a wide range of operating parameters. Such spacing has a substantial effect, particularly at high densities on fringing flux patterns such that the resolution of the sensing and recording on a record medium is significantly affected. Unfortunately, the interaction of many parameters, especially with the thin, closely spaced discs, which are in use today, have a substantial effect on the predictability and maintainability on such desired constant spacing. Such parameters include the relative speed between the record medium and the transducer, and the interior of the surface areas surrounding the transducer, and disc storage substrate parameters, such as flexibility and thickness. In addition, given the very tight spacing margins in present use between a transducer and the medium, even temperature and humidity can have a significant effect on variations in medium to transducer spacing.
Prior attempts to solve this problem have been both complex, expensive, and space-consuming. For example, in U.S. Pat. No. 3,178,719, a flexible magnetic disc is mounted in close proximity to a flat air bearing surface of an annular plate referred to as a Bernoulli plate and is rotated at a relatively fast speed causing the disc to assume a stable position. A number of magnetic heads are included in the plate, and a partial vacuum forms around small areas of the disc around the magnetic heads by a vacuum pump which is included. Obviously, this is a complex and expensive approach. A simpler apparatus includes a Bernoulli plate with a groove which is open to the disk and is readily disposed along the disc; convex surfaces are located on either side of a head, generating a pull-down force on the disc in the region near the groove. Once again, this is an expensive approach requiring considerable investment in additional parts.
A more recent approach in U.S. Pat. No. 4,578,727 describes a contact type recording apparatus in which a flat air bearing surface surrounds an elongate opening to a negative pressure cavity with the record and playback head arranged in the cavity. The use of the cavity will help to stabilize the disc surface at least when it is immediately adjacent to the transducer which is to access the data on the disc. As with the other approaches, this one consumes valuable vertical space.
Thus the problem of eliminating flow instability in a high speed rotating disc continues to need a solution.
The present invention relates to a device for stabilizing media for use in a hard disc drive during high speed rotation. More specifically, the present invention relates to disc media having a high speed rate of rotation in which means are introduced defined on the inner surface of the housing for adding stability to the disc and more specifically to the outer edge of the disc. Alternatively, to achieve these goals, the design of the disc may be modified.
In accordance with the present invention, at least in one embodiment, the outer edge of the disc surface is gradually thinned down to a sharp tip. In this way, the whirling air vortices which are normally formed at the disc tip are broken up or diminished. An alternative approach, the disc tip is gradually reduced in width and rounded at its outer edge, which also has beneficial results in terms of breaking up or diminishing the vortices of air which would otherwise cause instability of the disc.
In a further alternative embodiment of the invention, a flow obstruction is incorporated in the shroud adjacent the edge of the disc tip. This obstruction may comprise a small substantially rectangular insert extending from the inner edge of the housing, intermittently around the shroud circumference typically adjacent the edge of the disc tip where one of the vortices would normally be formed. The presence of this insert would tend to eliminate or prevent the formation of this air vortex or break the bigger vortices into smaller and local ones. This insert may further be used in combination with either a disc of normal thickness or a disc having a rounded or tapered edge as described above.
In yet another approach or embodiment of the invention, the inner surface of the housing, and more specifically the portion of the housing adjacent the ends of the disc which is also referred to as the shroud, incorporate grooves therein. These grooves which are roughly herringbone in shape, and would have their center near either the edge of disc in a single disc environment or mid-way between the disc in a two disc environment and would tend to channel the air away from the region where the whirling air vortex would normally be formed. This approach would also result in diminishing or eliminating the presence of the whirling air vortex.